The Federal Trade Commission is challenging the proposed combination of Staples and Office Depot, and the office supply companies say they plan to contest that decision.

Staples has proposed to buy rival Office Depot for $6.3 billion.

Staples Inc. and Office Depot Inc. said Monday that they will show that the FTC's decision is based on "a flawed analysis and misunderstanding" of the competitive landscape the companies deal with.

The pair argue that competition has become even tougher since Office Depot and OfficeMax merged in 2013 and that the FTC is contradicting itself because it said that the office supply market was highly competitive two years ago.

Office Depot Chairman and CEO Roland Smith says Staples and Office Depot plan to pursue legal options in order to complete the deal.